The microstructure, magnetic and mechanical properties of nanoheterogeneous (Fe0.5Co0.5)100-xCux alloys

FeCo alloys have attracted considerable interest due to the highest Curie temperature and magnetic induction intensity. However, there is rare investigations on nanoheterogeneous FeCo-based alloys. In this study, nanoheterogeneous (Fe_0.5Co_0.5)_100-xCu_x (x = 0–5) alloys are systematically designed, and their microstructural characteristics, magnetic behaviors, and mechanical properties are comprehensively investigated. The introduction of Cu atoms induces a notable refinement in the average grain size, decreasing from 52.3 μm for x = 0 to 24.3 μm for x = 5, accompanied by a reduction in the long-range order parameter. Through detailed microstructural analysis, the solid-solution limit of Cu in the alloy is determined to be approximately 2 at.%. When x > 2, Cu-rich nanophases with either twinned or twin-free face-centered cubic (FCC) structure precipitate within the matrix. With increasing Cu content from x = 0 to x = 5, the saturation magnetization exhibits only a marginal decrease of 0.57 %, while the Curie temperature drops by 2.7 %. Meanwhile, the coercivity shows a slight upward trend. Significantly, the tensile fracture strength demonstrates a linear increase, rising from 153 MPa for the Cu-free alloy to 400 MPa for the x = 5 composition. The compressive yield strength is also substantially enhanced, increasing from 278 MPa (x = 0) to 791 MPa (x = 5). Furthermore, the underlying mechanisms linking microstructural evolutions to the observed changes in magnetic and mechanical properties are systematically discussed. This research provides a potential avenue for the development of high-performance FeCo-based magnetic materials by establishing nanoheterogeneous microstructure.